1. Field of the Invention
The present invention relates to a switching power supply device which is disposed in an electronic equipment, generates direct current voltage having a first voltage value that is set in advance from power which is supplied from commercial power, and supplies direct current voltage based on the generated direct current voltage to devices disposed in the electronic equipment.
2. Description of the Related Art
Conventionally, in a regulated power supply circuit, such as a three terminal regulator, a chopper type regulator or the like, which is connected to a switching power supply device, in case where the regulated power supply circuit becomes an overload state by short circuit or the like of a load that is connected to an output terminal of the regulated power supply circuit, there is fear that the regulated power supply circuit generates heat and burns out. To solve the above described problem, various kinds of devices, methods, or the like have been proposed heretofore.
For example, a switching power supply device is disclosed in JP-A-2004-304898, which includes: a detecting circuit that is connected between an output terminal of a three terminal regulator and an output terminal of a main output circuit, detects that voltage of the regulator becomes lower than voltage of the main output, and outputs a detecting signal; an output circuit that outputs a power stop signal in response to the detecting signal; a second photo coupler that electrically insulates primary side and a secondary side and outputs the power stop signal to a PWM control circuit as a second feedback signal; and the PWM control circuit that outputs a signal to turn “OFF” a switching element as an “ON, OFF” control signal in response to the second feedback signal to the switching element to stop the switching power supply device.
However, in the above described switching power supply device, because it is necessary to dispose the detection circuit, the output circuit, the second photo coupler, and the like, production cost of the switching power supply device becomes high.